Some of wind power generation devices for generating electric power by rotating a main shaft with wind received by a blade are equipped with a speed-up gear. The speed-up gear increases the speed of the rotation of the main shaft to drive a power generator.
As illustrated in FIG. 9, a speed-up gear 202 includes a planetary gear mechanism 203 that receives the rotation of a main shaft 200 to increase its speed; and a high-speed stage gear mechanism 204 that receives the rotation increased in speed by the planetary gear mechanism 203 to further increase its speed. Besides, a high-speed shaft 205 for outputting the rotation increased in speed by the high-speed stage gear mechanism 204 is provided, and this high-speed shaft 205 is connected to a drive shaft (not shown) of a power generator, and a rotor of the power generator is attached to this drive shaft.
In the planetary gear mechanism 203, when an input shaft 203a integrally rotatably connected to the main shaft 200, to which a blade not shown is attached, is rotated, a planetary carrier 203b is rotated to rotate a sun gear 203d at an increasing speed via a planetary gear 203c. Then, this rotation is transmitted to a low-speed shaft 204a of the high-speed stage gear mechanism 204.
In the high-speed stage gear mechanism 204, when the low-speed shaft 204a is rotated, an intermediate shaft 204d is rotated at an increasing speed via a low-speed gear 204b and a first intermediate gear 204c, and the high-speed shaft 205 is rotated at an increasing speed further via a second intermediate gear 204e and an output gear 204f. 
Besides, as bearings for rotatably supporting the low-speed shaft 204a, the intermediate shaft 204d and the high-speed shaft 205 in the speed-up gear 202, rolling bearings (roller bearings) 206 to 211 are frequently used (see, for example, Patent Document 1).